1. Field of the Invention
The present invention relates to motor control, and in particular, to methods and systems for electronically controlling motors.
2. Description of the Related Art
HVACR (Heating, Ventilating, Air Conditioning, and Refrigeration) manufacturers conventionally design and manufacture multiple sizes of a given air conditioning, heat pump, furnace platform or other HVACR platform to accommodate different size spaces, buildings, installations, capacities, and different airflows. For example, a manufacturer may provide a variety of equipment sizes. For air conditioning the equipment may have ratings such as 1 ton, 2 ton, 3 ton, 4 ton, 5 ton, etc. For furnaces or heat pumps operating in the heating mode, the equipment may be rated in BTU, indicating the value of their heating output, such as 60,000 BTU 80,000 BTU, 100,000 BTU, etc. Different sizes of equipment generally require different size blower motors. The motors may be rated in horsepower, such as ¼ HP, ⅓ HP, ½ HP, ¾ HP, 1 HP, 1.5 HP, 2 HP, etc. However, each manufacturer may use a somewhat different blower. Further, for the same equipment rated output and given horsepower rating, some manufacturer's blowers may use or provide 100% of the rated horsepower capacity of the motor, some may use or provide 90% of the rated capacity, and some may even use 80% of the motor's rated capacity. Thus, the manufacturer's horsepower rating may not be a reliable indication of the actual horsepower needed in a replacement motor.
Further, HVACR manufacturers often design products for a specific static pressure (rated static pressure) and a specific RPM (Revolutions per Minute) in part by selecting a motor with the horsepower needed to produce the desired RPM at the static pressure used to rate their equipment. In general, the motor has been optimized for operation at that “rating” static pressure. However, when the HVACR equipment is installed in a home or commercial building, the static pressure is often different than that rated static pressure. For example, the actual static pressure may be significantly higher or lower than the rated static pressure the manufacturer's product was tested at to establish the equipment's rating. As the static load changes, a conventional motor may be operated at an RPM different than its optimal design point. This typically means the manufacturer must use motors with different horsepower ratings in order to accommodate even a relatively narrow range of different static pressures and one motor of any size may not be operating in an optimum condition in an application.
In view of the foregoing, distributors and manufacturers must carry inventory of a number of different motors at different horsepower ratings to ensure they are available when a demand arises. Moreover, because a contractor may not know what horsepower motor is actually needed to replace an existing motor, a contractor servicing HVACR equipment will typically need to carry an inventory of various motors to job sites to accommodate different loads, even when those loads do not vary widely. Failure to carry the needed motor results in wasted time as the contractor will have to leave the job site to purchase the proper motor. It should be noted that even replacing the installed motor with one of the same size may not produce proper operation, particularly in some severely restricted, high static pressure applications.